Method of making porous metal structures



6, 1941. J. T. MARVIN 2,241995 METHOD oF MAKING PoRoUs METAL STRUCTURES Filed Feb. 1, 1940 W @gf/O GAS , asY .asf db ofb;

NON OXlDlZ/NG GAS INVENTOR Patented May 6, 1941 gtric DIETHOD OF MAKING POOUS METAL STRUCTURES John T. Marvin, Dayton, Ohio, assgnor to General Motors Corporation, Detroit, Mich., a corporation oi' Delaware Application February 1, 1940, Serial No. 316,747

14 claims. (c1. 29-189) This invention relates to a method for impregnating highly porous metal matrices made from sintered metal powder and is particularly concerned with the method wherein a `substantial portion of impregnating metal is mechanically forced into the pores of thematrices.

An object of the invention is to provide a method for impregnating a porous metal sponge made from sntered metal powder wherein a low melting powdered impregnating metal is `spread on .the sponge and is mechanically forced into the pores of the sponge and is then subsequently heated for causing integration of the impregnated metal powder' whereby the impregnated metal is mechanically held within the pores of the sponge.

It is a further object in some cases to provide suflicient metal powder upon the matrix or sponge so that upon subsequent heating an overlay is provided above the surface of the sponge.

It is a still further object in some cases to adjust the mechanism for compressing the low melting metal powder into the matrix in such a manner that the high points of the matrix are simultaneously attened or mushroomed and the matrix is thereby sized.

In carrying out the above objects it is another object in some cases to provide pressure rolls for rolling the impregnated metal matrix after the heating step or steps in order to further compress the material.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing wherein preferred embodiments of the present invention are clearly shown.

In the drawing: y

Fig. 1 is a diagrammatic view showing apparatus which may be used to carry out the method described herein.

Fig. 2 is an enlarged cross sectional view showing a porous metal matrix bonded to a steel back,

Fig. 3 is a view similar to Fig. 2, wherein the matrix has been impregnated with metal powder and has been Yrolled sol as to flatten the high points of the matrix.

Fig. 4 is a view similar to Fig. 2 wherein the article has an overlay of the impregnated metal thereon.

derstood that this luxing step facilitates the im.-

Fig. 6 is a view showing diagrammatically another type of apparatus for impregnating and forming an overlay on porous metal sponge; and

Fig. 7 is a view taken on the line 1--1 of Fig. 5, showing the means provided for preventing the molten impregnating metal from flowing off the surface `of the matrix.

In Patent No. 2,198,253, assigned to the assignee of the present invention, a method is described wherein a highly porous metal matrix may vbe provided that is bonded to a steel supporting back or the like. In the above referred to application reference is made to a method for impregnatng a matrix with a soft bearing metal and it is to this step that the present invention is particularly directed. In Patent No. 2,198,253, it is proposed to immerse the matrix in molten impreg-y lowing the method described in vPatent No.

2,198,253. While the drawing shows apparatus for impregnating porous metal bonded to steel,

it is obvious that similar expedients could be resorted to for impregnation of porous metal bodies which are not bonded to steel in which case the porous metal bodies would necessarily have to be supported upon a non-porous' nonadhering body.A A method for making highly porous metal bodies which are not bonded to steel is described in Patent No. 2,157,596, assigned to the assignee of the present invention,

The method -described herein is particularly applicable to `the impregnation of highly porousv metal bodies wherein a simultaneous sizing of the porous metal layer is desired. As shown in Fig. 1, a porous metal matrix 20i preferably bonded to a steel supporting back22 is preferably passed under a fluxing mechanism' 24 and a suitable ux such as ammonium chloride, zinc chloride, resin and alcohol or any of the commercial uxes is sprayed into the matrix, or the ux may be mixed in the dry state with the powdered metal, such fluxes as ammonium chloride or resin, being suitable for this purpose. It is to be unpregnation, although the step in itself is not always necessary provided a clean matrix is provided. After being iluxed, the porous metal matrix 20 on strip 22 passes under a hopper 26 which contains powdered metal 28. The metal 28 is preferably lead, lead-tin, lead-antimony, lead-tin-antimony, tin, antimony, and combinations thereof or any other suitable soft metal. The metal powder 28 in hopper 26 falls upon the surface of the matrix by gravity and is smoothed into a uniform layer thereon by a smoothing device 32. 'I'he powdered matrix 20 supported .on strip 22 next passes between a pair of pressure rolls 34'which compress the powdered metal into the pores of the matrix, substantially filling 'the same and, if desired, the rolls 34 may be set in such a manner as to cause compression of the matrix layer itself, as noted in Fig. 3. In other words, the peaks of the matrix 'are flattened and mushroomed to further lock the powder 28 within the pores of the matrix and to make the matrix of Puniform thickness. If desired,- the strip with the powder thereon may be vibrated, either mechanically or magnetically to cause a 'portion of the powder to flow into the pores by causing the powder which is held within the pores of the matrix 20, to become molten. Non- -oxidizing gas should be supplied to the furnace to prevent any oxidation of the soft metal powder upon heating thereof. The pressure ofA the nonoxidizing gas should be sufilcient to cause a slight leakage thereof from the entrance and exit of the furnace. The impregnated strip next passes through a water cooled chamber 40 where the impregnated metal is chilled and solidified withirr the pores of the matrix 20. The strip' passes out Another method of applying the overlay contemplates the application of the overlay metal in sipated during the heating step.

of the chamber and then may be compressed .by roll 42 if desired. This last step is optional and may or may not be resorted to according to the particular material desired. If it is desired to provide an overlay of soft metal above the matrix the apparatus, as shown in Fig. 5, may be used wherein the strip passes through a similar l process, as shown in Fig. l, and upon cooling,

passes under a second hopper 44 with additional r f ture.

Fig. 6 shows still another type of apparatus matrix metal. -In this case the second. hopper 50 is provided4 which uniformly distributes additional metal powder on the surface of the strip after the flrst layer of metal powder has been compressed into the pores of the matrix. In this case, a furnace 52 is utilized to melt and integrate ,the overlay metal with the impregnated metal.

Expedients, such as sides 48, are provided to pre- Vwhich may be used to.form an overlay on the vent dissipation of the molten overlay layer chilled in the cooling chamber 54.

the molten state upon the impregnated surface of the matrix. Apparatus for accomplishingthis method is not shown as it is well known in the ar The matrix layer is preferably formed from metalpowder of fairlyl large mesh size, forexample,` to 200 mesh wherein each particle of metal is preferably spherical in shape. Thus when the matrix has been formed the pores thereof are of a maximum size and the entrance to the pore cavities and the pore cavities themselves are more or less uniform and devoid of overhanging ledges. .When a matrix is formed from spherical powder of this type it is more facile to rollthe metal impregnating powder into the pores, although it is to be erstood that any type of metal powder can be utilized with a com'- mercial degree of success, such powders falling into the classes of comminuted materials, electrolytic powders, reduced oxides, and the like. Spherical powders are made by well known methods, such as by atomizing molten .metals etc. The impregnating powder is preferably of a much smaller mesh than the powder used to form the matrix. Thus if a 150 mesh powder is used in the matrix layer, it is preferable to' use Z50-300 mesh soft metal powder, since it is a relatively simple matter to cause the fine impregnating powder -to flow into the pores when the sunface entries of thel pores are of considerably larger size than the cross section of the particles of impregnating metal powder. This fact coupled with' the mechanical forcing of the powder into the pores tends to insure substantially complete impregnation. When flux is used the flux is `dis- As preferred in .the majority of cases, the heating and cooling operations are carried out in non-oxidizing atmospheres and it is preferable to use soft metal powders substantially free from oxides since these oxides tend to hinder the wet-y ting action of the molten metal and .thereby hinde'r the flowing of the metal in the molten state within the pores of the matrix.

selected fr om the classes including copper, copper-tin, copper-tin-zinc, iron, iron-copper, aluminum, aluminum-copper, copper-nickel, tinnickel, and in fact vany of the metal powders, or combinations thereof, which form a matrix have ing the desired composition, texture and struc- The impregnating metalpowder obviously must be of lower melting point than lthe metal matrix and this fact is the only limiting requirement on fthe powder, although for obvious reasons low melting point powders such as tin,.lead and antimony, either as separate powdersA or pre-alloyed powders, are preferred.

The rolling step accomplishes the dual purpose of mechanically forcing the `metal powder into the pores of the matrix and also sizing the matrix layer .to the desired lthickness. This sizing step which oc s substantially simultaneously with the mechanical forcing of the metal powder into the matrix causes a locking action of the matrix on the powder whereby the metal powder upon becoming molten fills the pores and then upon freezing is mechanically held therein even though no alloying action vtakes place between the impregnating metal and the metal of the matrix. In this connection it should be noted that when the impregnating metal has a dissolving action upon the metal of the matrix, for example, a. copper matrix impregnated with a high tin content metal, that the heating step should be carried out at a suiiiciently low temperature and for a sufficiently short time to prevent dissolution of the matrix due to the dissolving action of the impregnating metal. In each case, therefore, it is apparent that the heating step need only be carried out at a, temperature slightly above the melting point of the impregnating metal.

While the process as illustrated is directed to a continuous process, it is obvious that an analogous procedure may be resorted in an intermittent process, wherein separate pieces of the porous metal matrix are used and wherein' the soft metal powder is spread in a uniform layer thereover and then forced therein. In other words, the method is quite well suited to a continuous or intermittent process of impregnation.

While the embodiments of the Ipresent invention as herein disclosed, constitute preferred forms, i-t is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. In a method for making composite material, the steps comprising: providing a highly porous matrix by sintering a loose layer of non-compacted metal powder upon a supporting member,

' ing point of the matrix to cause the metal powder to melt and iiow into the pores of the matrix whereby a composite article is produced having the matrix thereof impregnated with the soft metal.'

. 2. In amethod as claimed in claim 1 wherein the impregnated matrix is compacted after heatmg.

3. In a method as claimed in claim 1 wherein the matrix is uxed prior to the distribution of the soft low melting point metal powder thereon.

4. In a method for making composite material, the steps comprising: providing a highly porous matrix bonded to a non-porous supporting member by sintering a loose layer of non-compacted metal powder upon said supporting member, distributing a uniform layer of soft low melting point metal powder upon said matrix surface, compressing the metal powder to force a substantial portion thereof into the pores of fthe matrix, and then heating the supporting member, matrix and metal powder under suitable conditions and at a temperature above the melting point of the metal powder and well below the melting point of the metal of the matrix for causing the metal powder to melt and now within the pores of the matrix,.whereby the matrix is impregnated with the soft metal.

5. The method as claimed in claim 4 wherein tributing a soft low melting point metal powder the compression of the metal powder is accomplished by passing the supporting member with the powder thereon between pressure rollers whereby the powder is forced into the pores of the matrix and the high points of the matrix are simultaneously mushroomed so that the matrix is of a substantial uniform thickness throughout.

6. The method as claimed in claimd wherein suincient soft metal powder is distributed upon the matrix to provide an overlay after the heating step. A

7. The method as claimed in claim 4 wherein additionalmetal powder is applied subsequentto the compressing step and before the heating Steps v l im .LL

u. In a continuous method for making composite strip stock, the steps comprising: continuously providing a highly porous matrix bonded to a non-porous strip of steel or the like by continuously sintering a loose layer of noncompacted metal powderupon said. strip, continuously distributing a soft low melting point metal powder upon said matrix layer, continuously compressing the metal powder to force a portion thereof into the pores of the matrix, and then heating the strip under suitable conditions at a temperature above the melting point of the metal powder and well below the melting point of the metal of the matrix to cause the metal powder to melt and ow within the pores of the matrix and whereby strip stock is formed wherein` the matrix isimpregnated with the softbearing metal.

9. The method as claimed in claim 8 wherein sufficient soft low melting point metal powder is distributed upon the matrix to provide an ogrerlay of the metal powder after the heating s ep.

10. The method as claimednn claim 8 wherein the compressing step is carried out under conditions of pressure suicient to cause a.' mushrooming effectvupon the matrix metal at the high lpoints thereof to mechanically lock the metal powder within the pores.

11. In a method of making composite stock including a layer-of highly porous metal'made from sintered non-compacted metal powder bonded to a layer of a more dense metal wherein the porous metal layer is impregnated with a soft bearing metal, the steps comprising; mechanically forcing powdered soft bearing metal into the interstices of the porous metal layer for simultaneously impregnating the porous metal layer and-for sizing said layer, and then heating the composite stock to a temperature suiiicient to melt the soft bearing metal but well below the melting point of the porous metal whereby the soft bearing metal and the porous metal are integrated'.

12. In the method for making composite maf terial including a relatively thin highly porous metal layer made from non-compacted sintered upon said matrix, and then mechanically forcing said powdered soft metal into the pores of the matrix for substantially filling the 'pores of the matrix with soft metal. f

14. In the method of making composite material the steps comprising, providing a highly porous metal matrix by sintering together a. loose layer of non-compacted metal powder. dis- 4f f 2,241,095v

tributing a soft low melting' metal powder upon mtrixfwhereby the soffr metal powder is inelsaid matrix, and then forcing said soft low chanically locked Within the matrix due to the melting metal powder into the pores of the -mushrooming effect at the high points of the matrix by means of pressure applied for submatrix.

A stantially filling the pores of the matrix with 5 I JOHN T. MARVIN.-

the soft metal and for simultaneously sizing the' 

